The improvised indie drama Your Sister’s Sister, from filmmaker Lynn Shelton, is a human story of grief and romance, and finding humor in unlikely places. Jack (Mark Duplass) is an emotionally unstable slacker, still reeling from the death of his brother Tom, a year later. When Tom’s ex-girlfriend Iris (Emily Blunt) offers up her family cabin on an island in the Pacific Northwest, Jack runs into Iris’ sister Hannah (Rosemarie DeWitt), who herself is reeling from the abrupt end of a long-term relationship and looking for solace.

At the film’s press day, actor Mark Duplass spoke to Collider for this exclusive interview about how he came up with the idea for the film which he brought to Lynn Shelton, what he was looking to do with this character, improvising with Emily Blunt and Rosemarie DeWitt, the easiest and hardest scenes to improvise, and what he likes about collaborating with Shelton, as a filmmaker. He also talked about working with Kathryn Bigelow on her Osama Bin Laden film (tentatively titled Zero Dark Thirty), what he looks for in acting roles, what he enjoys about doing the FX series The League, and what he’s looking to do next. Check out what he had to say after the jump:

Collider: How did Your Sister’s Sister come about? You came up with the initial idea and brought it to Lynn Shelton?

MARK DUPLASS: It was something I had hanging around on my computer. I have a document of a bunch of movie ideas, some good and some terrible. I was thinking, “What could be a good fit for me and Lynn?,” ‘cause I just loved making Humpday. I wanted to do it again and try to make a little bit of a bigger movie that could reach out further and incorporate some incredible movie stars, and this seemed like the right fit. So, I pitched it to Lynn, and she had a hole in her schedule and I had a hole in mine, and it just worked out.

Was there something specific that sparked this idea for you?

DUPLASS: Yes. I wanted to do something different, as an actor. I wanted to do something that was 50% different, in particular. I didn’t want to change it drastically. To me, with this film, I play a character that I’ve played before, to a certain degree. He’s a down-on-his-luck everyman. But, I also wanted to play someone who had just had something terrible happen to him, so there’s this really dark emotional root to him. This guy has just lost his brother. It was the concept of, “What would it feel like to make a movie that, at its core, is a Shakespearian bed-switching love triangle with hijinks and buffoonery, and all that stuff that Three’s Company did so well, but with a real emotional core to it, and that comedy-drama blend?” When the initial idea came up, it was going to be between a guy, his best friend who’s a girl, and her mother. Lynn was immediately like, “No, let’s do it as sisters,” and I was like, “Sure.” I learned just a shit-ton about sisters through doing this movie. My brother, Jay, and I are very close and very intimate, but there’s something about these sisters – and I don’t know if it’s all sisters – that was just really cool for me to watch.

Was it difficult for you to relate to being the guy who didn’t have a relationship with his brother?

DUPLASS: Yes, but the feeling of regret and the feeling of how lost I would be, if I didn’t have Jay, was enough to care me through that, basically. That was an anchor for me to connect to. That, in many ways, is the same emotion as playing someone who’s lost a brother who was close to them and they miss them. Someone who’s lost a brother who they weren’t close enough with and wishes they had been closer to is a similar sadness, I think.

What was it like to work with Emily Blunt and Rosemarie DeWitt?

DUPLASS: They’re fantastic, and I’m not just saying that in a press way that you have to say. They are fantastic people, and they’re really sensitive and loving. That’s what makes them great actors, I believe. They loved these characters, and their attention to human nature and the odd personal interactions of life make them great. We were all really co-collaborators on this movie. When you’re improvising a film like this, you’re taking part in creating the story, every minute. We would talk about it after work, at dinner together, and rework scenes. They both said they were worried about their ability to improvise, but you wouldn’t have known it.

When you work with people who aren’t used to improvising in that way, do you learn things about acting from that experience?

DUPLASS: Yes, 100%. I call it, “Their movie star shit that I learned.” I’m a narrative-minded actor. I’m thinking of the story. I’m not worried about whether the camera is on the right side of my face, or where the camera is. I’m just going for the story. And Rose and Emily, in particular, have this way of employing naturalism, but also knowing how to turn the right way so that the light catches them and the camera is there. I was like, “Oh, shit! This is a whole new ball game.” I learned a lot from them.

In developing this character and talking about who he was beforehand, were there things that you specifically wanted to bring to him, as a person?

DUPLASS: Yes. I like the idea of someone who makes a lot of jokes when they’re dealing with death, and doesn’t know how to deal with it, so you downplay it and cast it off. I like the idea that this guy was once really charming, and he could win people over. I do win over Rose, in that first big drinking scene. Part of that is Jack winning over Hannah, but that was the first night that Rose and I ever hung out and my job was to charm her and win her over, which is hard. I like the idea that this guy who seemingly has very few life skill sets, at the moment, and very little going for him, has this promise of this person that he either was or could be. He’s not totally dumb. He’s got some charm and can win them over. He’s this raw, undeveloped thing. I like the idea that you could watch him go from that critical point where he’s either going to be depressed for the rest of his life over the death of his brother and go down the bad wormhole, or he’s going to turn it around a little bit.

Was it important for you to find the balance between this guy being lost, but having audiences still want to root for him?

DUPLASS: Yeah. He’s not very likeable, on the surface. Granted, a large part of that is due to Lynn and the editor, Nat Sanders, who craft that performance in the edit room. It was just towing that line between this guy being fucking hopeless and him maybe getting it together.

Was there a scene that was easiest for you to improvise, and one that was the most difficult?

DUPLASS: The easy one was that first scene with Rosemarie. That was easier than I thought it was going to be. It’s the type of scene that I feel like I’m good at. I had five things I needed to hit, story wise. It was the perfect combination of my skills as a writer and as an actor. I had to concurrently improvise the scene, as an actor, but also write it, as we were going. That was a really fun scene. The harder scene for me was the big blow-up scene between me and the girls, towards the end of the film. It was really interesting because the plot points in that scene – and we had discussed it early on – were like soap opera plot points. The form of this film is, in many ways, like a soap opera. So, it was about finding a way to underplay that and make it feel natural and human while, at the same time, honoring the big things that were happening. I struggled with that a little bit, at the front. Luckily, the girls were dead on in it, and they carried me through that one.

What is it about your collaboration with Lynn Shelton that you like so much, that makes you think about ideas for projects that you can do together?

DUPLASS: There’s an alchemy with people that’s hard to understand. I don’t think she and I can intellectually ferret it out, exactly. We really like each other. We laugh at the same things. We both bring very specific skill sets to the table. I know that Lynn is open enough not to be challenged by me, as a collaborator. I know that I can trust Lynn with any of the content that’s happening. I can walk off this movie after we shoot and know that she and (editor) Nat Sanders are going to put together a great movie. It just really works.

With all of the projects you have on your plate, what was it about the Kathryn Bigelow movie about Osama Bin Laden that made you want to do that?

DUPLASS: I want to work with great directors, and that’s just it. I am obsessed with The Hurt Locker and her. What she is doing is employing naturalism to these big high-concept political movies. If you look at the performances in this movie, they feel like the performances in my movies. That made me feel like, “Okay, I can take what I do, to a certain degree, and be additive to her process. It won’t be diametrically opposed to what I do, on a daily basis.” And it turned out to be a great fit.

Who are you playing in the film?

DUPLASS: I can’t talk about that. I am contractually signed to be quiet.

Especially when you’re doing projects that are other people’s, what do you look for?

DUPLASS: A lot of it is as much life experience as it is creative fulfillment. Doing Darling Companion with Lawrence Kasdan and all those actors was about being with them for six weeks. I would have shot any script. It didn’t matter. I wanted to go be with my heroes and milk them for information during dinner and hang out with them. People Like Us was a fantastic script. They only needed me for two weeks time and I was in town, so I got to know some new people and be a part of a great movie and walk away with a little time commitment. It was the same thing with when I did Greenberg with Noah Baumbach. It was a week’s worth of work, for me to be with some people that I really admire, who are my peers. It’s all different kinds of reasons. Some of it is practical like, “I have two weeks off between shooting The League and when I have to start a writing job. Here’s something. I can do this.” Some of it is just this desire to make stuff. I’m just deeply compelled. We could go to a therapist and try to figure it out. I don’t know what it is. I just have the compulsion.

Is it fun to have the diversion of The League, where you can develop a character over a longer period of time?

DUPLASS: That’s fun. The most fun thing about The League, for me, is that I’m like the dad in that group. I’m actually not as good at slam-dunking the big jokes, but I’m really good at keeping everybody corralled and organized. I can take the ball down the field, and then pass it off to Nick Kroll and know that he will deliver a joke in a way that I’ll never know how to do. It’s this fun, collaborative teamwork thing. It’s fun working on something that has very little emotional content. A lot of the stuff I work on is very complex and taxing, and that’s a fun joke bag. It’s like being in an acting class. It’s really loose and easy. I like that, as a counterpoint to some of the other stuff I do.

Do you know which thing you’ll do next?

DUPLASS: Once I get through this big stretch of promotion, I’ll go into The League in August. I’m writing a bunch of scripts right now, for me and Jay to direct, but also some scripts for other people to direct. That’s a little bit of our bread and butter, too. And then, I’m looking for the right, really interesting acting role for the early part of next year. I don’t know what that’s going to be yet. I’ve definitely realized now, through these movies this summer, I can get better jobs, so I’m going to try to figure out how far I can take that.

Is there a dream role that you’d love to do, or a script that you’d love to make, at some point?

DUPLASS: I have a couple of things, none of which I can really talk about because they’re in development, at the moment. I love Eternal Sunshine of the Spotless Mind. That was a really special movie to me. Safety Not Guaranteed has some similarities to that. I love the humanness side to genre films, whether that’s a thriller or an action movie or a sci-fi movie. When you can take a really awesome, classic Steven Spielberg story and inject a serious dose of humanity and feelings into it, that’s my favorite combination.

Wearing so many hats, in front of and behind the camera, is there one that you feel like you most identify with?

DUPLASS: That’s a really good question. I don’t know. I love doing them all, right now. I feel like, if I’m being honest with myself, my biggest skill set is as a writer ‘cause I can do that quickly and I’m really grounded in story structure. Part of my success as an actor, is that I know story well. Part of my success as a director, is how well I know story. Same thing, as a producer. It all begins and ends with me as a story creator. But, I love doing it all, right now.

COLLIDER participates in various affiliate marketing programs, which means COLLIDER gets paid commissions on purchases made through our links to retailer sites. Our editorial content is not influenced by any commissions we receive.